Syntactic foams with improved water resistance, long pot life and short demolding times

ABSTRACT

This invention relates to syntactic foams comprising the reaction product of a liquid diphenylmethane diisocyanate component, with an isocyanate-reactive component, a filler having a density of less than 1 g/cm 3, and at least one organo-metallic catalyst. This invention also relates to the use of these syntactic foams for insulating pipes.

BACKGROUND OF THE INVENTION

This invention relates to syntactic foams, a process for the preparationof these syntactic foams, pipes insulated with these syntactic foams,and a process for the production of these pipes insulated with syntacticfoams.

Rigid foams and processes for their production are well known in theart. Such foams are typically produced by reacting a polyisocyanate withan isocyanate reactive material such as polyol in the presence of ablowing agent. A lot of the blowing agents used in the past are nolonger acceptable, and the ones developed in recent years are availableat much higher costs. Furthermore, the state of the art rigid foamsprepared with blowing agents do not exhibit the high compression setrequired when foams are used, i.e. in applications like deep seapipeline insulation.

In recent years, the substantial increases in costs of the basicmaterials used to make foam, has encouraged the development and use offiller materials to reduce the amount of the basic materials used andthe weight of the finished materials. One of the suggested fillermaterials and insulating materials utilizes hollow microspheres.

The expression “syntactic” as used herein refers to the use of hollowspheres in a polymer matrix to produce a cellular material.

Expanded microspheres consisting of a synthetic thermoplastic resinshell that encapsulates a liquid blowing agent are known. See, forexample, U.S. Pat. Nos. 4,829,094, 4,843,104 and 4,902,722. U.S. Pat.Nos. 4,829,094 and 4,843,104 disclose a syntactic-polymer foamcomposition having a low density filler containing free flowingmicrospheres.

U.S. Pat. No. 4,916,173 discloses a polyurethane syntactic foamcompositions for millable modeling stock applications. These PUsyntactic foam compositions have high glass transition temperatures andlow coefficients of thermal expansion, and are prepared from a polymericisocyanate, an amine-based polyol, a polyether triol, molecular sievematerial and hollow microspheres. The foams are described as a solidpolymer matrix. These compositions are based on polymethylenepoly(phenyl isocyanate) and result in low physical properties (i.e.tensile strength, elongation, etc.) which may be suitable for modelingstock applications, but not for the more demanding requirements in deepsea pipeline insulation

A solid polymer matrix is disclosed by U.S. Pat. No. 4,959,395. Thispatent describes bulk polymerization of cycloolefin monomers byring-opening polymerization wherein the microencapsulated blowing agentsaid in filling molds during RIM procedures such that both surfaces ofthe article being molded remain in contact with the mold surfaces.

U.S. Pat. Nos. 4,303,729 and 4,303,736 disclose the use of hollowplastic microspheres as filler materials in plastics. The microspheresdescribed by these two are generally large diameter microspheres, i.e.in the range of 200 to 10,000 microns. These microspheres can be madefrom low heat conductivity plastic compositions and blown with a lowheat conductivity gas to make improved insulation materials andcomposites.

Hollow microspheres having lower loadings of 2 to 5% by weight of thetotal composition are disclosed by U.S. Pat. No. 4,038,238. Low densitypolyurethanes are produced from rapid-setting polyurethane-formingcompositions containing light weight hollow spheres or microballoons anda liquid viscosity reducing agent.

A rigid syntactic foam comprising glass microballoons is disclosed byU.S. Pat. No. 4,082,702. These foams are obtained by mixing an organicpolyol, a polyisocyanate, a catalyst for the reaction of the polyol andthe polyisocyanate, microballoons, and a flame retardant foam having abimodal cell structure.

U.S. Pat. No. 3,510,392 discloses glass nodules in cellularpolyurethane. The polyurethane comprises a polyol and/or polyesterreacted with an polyisocyanate, and water during crosslinking to providea gaseous blowing agent. The reactive components are homogeneously mixedin a suitable mixing device with a surfactant and catalyst to controlthe rate of reaction. Cellulate glass nodules are added to thehomogeneous mixture in the bottom of a mold cavity which is then closedand foaming occurs. These are suitable for building panels having acontinuous polyurethane phase and a discontinuous phase (i.e. cellularglass nodules).

Syntactic rigid PUR/PIR foam boardstock is described by U.S. Pat. No.6,166,109. These hollow microspheres are filled with a hydrocarbon, airor vacuum, to introduce uniform cell geometries in the foams. Themicrospheres, which have an average diameter of 0.01 to 60 microns, areencapsulated with a closed cell polyurethane foam. Foams in the examplesare based on a polyester, a surfactant, catalysts, water, achlorofluorocarbon blowing agent and a polymethylenepoly(phenylisocyanate). These syntactic rigid foams have a bimodal cellstructure.

The JP 4257429 reference describes the manufacture of foam sheets withsmooth surfaces which are useful for thermal insulators, packagingmaterials, etc. The foam sheets of this reference can be prepared byapplying a composition containing an organic polymer binder and a lowboiling point solvent sealed thermally expandable microcapsules on abase film, laminating a polyester film on the coated layer, heating todry and expand the coated layer and removing the polyester film. Theresultant foam sheets have uniform closed cells and a smooth surface.

Thermally insulating syntactic foam compositions are disclosed by U.S.Pat. No. 6,284,809. These foam compositions have thermal conductivitiesless than 0.120 watts/meter-° K and exhibit acceptable strength andbuoyancy characteristics for subsea applications at depths of up toabout 10,000 ft. These syntactic foams are formed from 40-45 volume % ofa resin binder containing hollow microspheres which comprise betweenabout 55 and about 60 volume % microspheres and between about 65 and 50volume % minispheres. Microspheres are described as having a diameterbetween 1 and 100 microns, and minispheres are defined as havingdiameters from ⅛ inch up to ⅜ inch.

It has now been found that a syntactic foam can be prepared having longpotlife (i.e. 4 minutes) and short demolding times (i.e. less than 10minutes), excellent hydrolytic stability combined with low waterabsorption and very good physical properties, i.e. high elongationcombined with high tensile strength at microsphere filler levels of10-70%. The syntactic foams of the present invention require apolyurethane composition comprising (1) a liquid diphenylmethanediisocyanate, (2) an isocyanate-reactive compound comprising a blend ofone or more low unsaturation difunctional polyoxypropylene polyethers,one or more polyoxypropylene polyethers wherein the starter comprises atleast one nitrogen atom, and one or more polyoxypropylene polyetherswherein the starter comprises an organic compound having at least threehydroxyl groups, and, optionally, one or more low molecular weight diolsand/or triols, (3) a filler having a density of less than 1 g/cm³, and(4) at least one organo-metallic catalyst.

SUMMARY OF THE INVENTION

This invention relates to syntactic foams, to a process for thepreparation of these syntactic foams, to pipes insulated with thesesyntactic foams, and to a process for the production of pipes insulatedwith these syntactic foams.

Syntactic foams of the present invention comprise the reaction productof:

(1) a liquid diphenylmethane diisocyanate having an NCO group content offrom about 10 to about 33.6%, preferably 15 to 32% and most preferably20 to 30%, and a viscosity from about 10 to about 5,000 mPa·s at 25° C.,preferably 10 to 3,000, and most preferably 10 to 1,000 mPa·s at 25° C.;with

(2) an isocyanate-reactive component comprising:

(a) at least 10% by weight (preferably from 10 to 30% and mostpreferably from 10 to 20%) by weight of one or more polyether polyolshaving a functionality of about 2 to about 4, preferably about 3, a(number average) molecular weight of 200 to about 8,000, preferablybetween 240 and 4,000 and most preferably about 450 to 500, and ahydroxyl number of 14 to 1,120, preferably of about 42 to about 700, andmost preferably about 336 to 374, wherein the starter for said polyetherpolyol contains at least one amine group and said starter is alkoxylatedwith 100% by weight of propylene oxide;

(b) at least 20% (preferably 30 to 80% and most preferably 40 to 60%) byweight of one or more low unsaturation (preferably having less than 0.01meq/g unsaturation) polyether polyols having an OH functionality ofabout 2, a molecular weight of about 250 to about 8,000, preferably fromabout 500 to about 3,000 and most preferably about 1,000 to 2,000, and ahydroxyl number of about 14 to about 448, preferably about 37 to about224 and most preferably about 56 to about 112, wherein the startercomprises water or an organic compound with two hydroxyl groups and saidstarter is alkoxylated with 100% by weight of propylene oxide;

(c) at least 20% (preferably 30 to 80% and most preferably 40 to 60%) byweight of one or more polyether polyols having an OH functionality ofabout 3 to 6 (preferably 3 to 4) and a molecular weight of about 400 to3,000 (preferably of about 500 and 1,000 and most preferably of about600 to about 800) and a hydroxyl number of about 56 to about 840(preferably about 168 to 448, and most preferably 210 to 373), whereinthe starter comprises an organic compound with at least three hydroxylgroups and that is free of amine groups, and the starter is alkoxylatedwith 100% by weight of propylene oxide; and, optionally,

(d) up to 10% by weight of one or more low molecular weight diols and/ortriols having an equivalent weight of from 31 to 99,

wherein the %'s by weight of (2)(a), (2)(b), (2)(c) and (2)(d) totals100% by weight of component (2);

(3) from 10 to 70% (preferably from 15 to 30%) by weight, based on thecombined weight of components (1), (2) and (3), of a filler having adensity of less than 1 g/cm³ (preferably glass hollow spheres); and

(4) at least one organo-metallic catalyst in an amount of about 0.001 toabout 1% by weight, based on 100% by weight of (2);

wherein the relative amounts of components (1) and (2) are such that theisocyanate index is from about 90 to about 120, preferably from about 95to about 110.

The process of preparing the syntactic foams of the present inventioncomprises reacting:

(1) a liquid diphenylmethane diisocyanate having an NCO group contentand a viscosity as described above; with

(2) an isocyanate-reactive component comprising:

(a) at least 10% by weight of one or more polyether polyols having afunctionality, molecular weight and a hydroxyl number as describedabove, wherein the starter for said polyether polyol contains at leastone amine group and said starter is alkoxylated with 100% by weight ofpropylene oxide;

(b) at least 20% of one or more low unsaturation polyether polyolshaving an OH functionality, a molecular weight and a hydroxyl number asdescribed above, wherein the starter comprises water or an organiccompound having two hydroxyl groups and said starter is alkoxylated with100% by weight of propylene oxide;

(c) at least 20% by weight of one or more polyether polyols having an OHfunctionality, a molecular weight and a hydroxyl number as describedabove, wherein the starter comprises an organic compound with at leastthree hydroxyl groups and that is free of amine groups, and said starteris alkoxylated with 100% by weight of propylene oxide; and, optionally,

(d) up to 10% by weight of one or more low molecular weight diols and/ortriols as described above, wherein the %'s by weight of (2)(a), (2)(b),(2)(c) and (2)(d) totals 100% by weight of component (2);

(3) from 10 to 70% by weight, based on the combined weight of components(1), (2) and (3), of a filler having a density of less than 1 g/cm³(preferably glass hollow spheres); and

(4) at least one organo-metallic catalyst in an amount of about 0.001 toabout 1% by weight, based on 100% by weight of (2);

wherein the relative amounts of components (1) and (2) are such that theisocyanate index is from about 90 to about 120, preferably from about 95to about 110.

The present invention is also directed to a pipe insulated with thesyntactic foam as described hereinabove, and to a process for theproduction of a pipe insulated with this syntactic foam. The process forthe production of a pipe insulated with the syntactic foam comprises:

(I) placing a steel pipe in the center of a cylindrical mold with thediameter of the mold being larger than the diameter of the pipe, whereinthe difference in diameter between the pipe and the mold determines thethickness of the syntactic foam to be applied;

(II) pouring a liquid polyurethane reaction mixture containing a filleraround the steel pipe in the mold, wherein said liquid polyurethanereaction mixture is formed by

(A) blending (3) a filler having a density of less than 1 g/cm³(preferably glass hollow spheres) with (1) a liquid diisocyanatecomponent and/or (2) an isocyanate-reactive component,

(B) adding (4) an organo-metallic catalyst to the isocyanate-reactivecomponent which may or may not contain a filler, and

(C) mixing the liquid diisocyanate component with theisocyanate-reactive component, wherein:

(1) said liquid diisocyanate component comprises liquid diphenylmethanediisocyanate having an NCO group content of from about 10 to about 33.6%and has a viscosity of from about 10 to about 5,000 mPa·s at 25° C., and

(2) said isocyanate-reactive component comprises:

(a) at least 10% by weight of at least one polyether polyol having afunctionality of about 2 to about 4, a molecular weight of about 200 toabout 8,000 and a hydroxyl number of about 14 to about 1,120, whereinthe starter for said polyether polyol contains at least one amine groupand is alkoxylated with 100% by weight of propylene oxide,

(b) at least 20% by weight of one or more low unsaturation polyetherpolyol having an OH functionality of about 2, a molecular weight ofabout 250 to about 8,000, and a hydroxyl number of about 14 to about448, wherein the starter comprises water or an organic compound with twohydroxyl groups and is alkoxylated with 100% by weight of propyleneoxide,

(c) at least 20% by weight of one or more polyether polyols having an OHfunctionality of about 3 to about 6, a molecular weight of about 400 toabout 3,000 and a hydroxyl number of about 56 to about 840, wherein thestarter comprises an organic compound with at least three hydroxylgroups and that is free of amine groups, and is alkoxylated with 100% byweight of propylene oxide, and, optionally,

(d) up to 10% by weight of one or more low molecular weight diols and/ortriols having an equivalent weight of from 31 to 99,

wherein the %'s by weight of (2)(a), (2)(b), (2)(c) and (2)(d) totals100% by weight of component (2);

(III) allowing the liquid polyurethane reaction mixture containing thefiller to cure to form a solid polyurethane containing a filler, whichencapsulates the steel pipe; and

(IV) demolding the polyurethane encapsulated steel pipe, therebyyielding a syntactic foam insulated pipe.

DETAILED DESCRIPTION OF THE INVENTION

The syntactic foams of the present invention are hydrolytically stableand have a high compression E-modulus. More specifically, the highcompression E-modulus is greater than 300 psi. These hydrolyticallystable syntactic foams can be exposed to water at temperatures of from 0to 40° C. for up to 10 years without degradation. These syntactic foamsalso exhibit a long pot-life, i.e. about 4 minutes, and short demoldingtimes, i.e. less than 10 minutes. In particular, at about the samehardness and density, a liquid diphenylmethane diisocyanate vs.polymethylene poly(phenylisocyanate) in combination with a lowunsaturation difunctional polyether polyol, the resultant syntacticfoams have higher tensile strength and elongation (about 50% more),higher tear strength (i.e. about 3 times higher), lower Taber abrasion(30 to 50% less), and considerably lower water absorption (25 to 50%less in fresh water, and 20 to 30% less in salt water).

Suitable liquid diphenylmethane diisocyanates to be used as component(1) in the syntactic foam of the present invention have an NCO groupcontent of from about 10 to about 33.6%, and a viscosity of about 10 toabout 5,000 mPa·s at 250. It is preferred that the NCO group content befrom about 15 to about 32% and a viscosity from about 10 to about 3,000mPa·s at 25°. Most preferred are liquid diphenylmethane diisocyanateshaving an NCO group content of from about 20 to about 30% and aviscosity from about 10 to about 1,000 mPa·s at 25°.

The liquid diphenylmethane diisocyanates can comprise up to 70%(preferably from 1 to 55%) by weight of the 2,4′-isomer ofdiphenylmethane diisocyanate, no more than 2% (preferably no more than1%) by weight of the 2,2′-isomer of diphenylmethane diisocyanate, andthe balance being the 4,4′-isomer of diphenylmethane diisocyanate, withthe sum of the 2,2′-isomer, the 2,4′-isomer and the 4,4′-isomer totaling100% by weight of diphenylmethane diisocyanate. Most preferred areliquid diphenylmethane diisocyanates that contain more than 90% of the4,4′-isomer.

Modified liquid diphenylmethane diisocyanates are also preferredisocyanates to be used in the present invention. These modified liquidisocyanates include allophanate-modified diphenylmethane diisocyanate,diphenylmethane diisocyanates comprising carbodiimide groups and/oruretonimine groups, and prepolymers which are the reaction product ofdiphenylmethane diisocyanate with a polyether polyol containing at least80% by weight of ether units derived from propylene oxide.

In accordance with the present invention, suitable isocyanate componentsto be used as component (1) in the present invention include (a)allophanate modified diphenylmethane diisocyanates, (b) carbodiimidemodified diphenylmethane diisocyanates, (c) uretonimine modifieddiphenylmethane diisocyanates, and (d) urethane modified diphenylmethanediisocyanates, as well as mixtures thereof. The liquid diphenylmethanediisocyanate adducts have an average functionality of about 2.0 to about2.3, and an NCO content of 10 to 32% by weight.

As used herein, the term “allophanate group” refers to the followingstructure:

As used herein, the term “uretonimine group” refers to the followingstructure:

As used herein, the term “carbodiimide group” refers to the followingstructure:

R—[N═C═N]—R

The isocyanates useful herein can be prepared by chemical modificationof monomeric diphenylmethane diisocyanate (MDI). Suitable modificationsinclude reactions with polyether polyols, diols or monoalcohols to formurethane and/or allophanate containing liquid MDI-derivatives or specialcatalysts to react isocyanate groups with themselves to formcarbodiimide and/or uretonimine containing liquid MDI-derivatives.

Suitable isocyanates are liquid MDI-derivatives containing carbodiimidegroups of the type described in U.S. Pat. No. 3,152,162, the disclosureof which is herein incorporated by reference; liquid MDI-derivativescontaining urethane groups of the type described, for example, in U.S.Pat. Nos. 3,394,164 and 3,644,457, the disclosures of which are hereinincorporated by reference; liquid MDI-derivatives containing allophanategroups of the type described, for example, in British Patent 994,890,Belgian Patent 761,616, and published Dutch Patent Application7,102,524, the disclosures of which are herein incorporated byreference.

It is also possible to use mixtures of the polyisocyanates describedabove.

In accordance with the present invention, at least a portion of theliquid diisocyanate component is preferably present in the form of aliquid diisocyanate adduct, such as a liquid diphenylmethanediisocyanate adduct containing allophanate groups, a liquiddiphenylmethane diisocyanate adduct containing carbodiimide groups, aliquid diphenylmethane diisocyanate adduct containing uretoniminegroups, or a liquid diphenylmethane diisocyanate adduct containingurethane groups. Suitable adducts include the following type ofcomponents:

Allophanate group-containing diphenylmethane diisocyanates include, forexample, those prepared according to the processes disclosed in U.S.Pat. Nos. 3,769,318, 4,160,080, 4,177,342, 4,810,820, 5,319,053,5,319,054, 5,440,003, 5,606,001, 5,663,272, 5,672,736, 5,859,163,5,917,083, the disclosures of which are herein incorporated byreference. Preferred allophanate modified polyisocyanates for thepresent invention have an NCO group content of from about 15 to 32%, andpreferably from about 20 to 29%.

Carbodiimide group-containing and uretone imine group-containingdiphenylmethane diisocyanates for the present invention include, forexample, those which may be prepared by oligomerizing diphenylmethanediisocyanates in the presence of known carbodiimidization catalysts suchas described in, for example, German Patentschrift 1,092,007, hereinincorporated by reference, U.S. Pat. Nos. 2,853,473, 3,152,162, and5,202,358, the disclosures of which are herein incorporated byreference, and German Offenlegungschriften 2,504,400, 2,537,685 and2,552,350, the disclosures of which are herein incorporated byreference.

Suitable prepolymers of diphenylmethane diisocyanate to be used ascomponent (1)(d) in the present invention include those liquidprepolymers which are the reaction product of diphenylmethanediisocyanate having an NCO group content of 10 to 25% and a viscosity of50 to 5,000 mPa·s at 25° C., with a polyether polyol containing at least80% by weight of ether units derived from propylene oxide. It ispreferred that these diphenylmethane diisocyanates comprise from 0 to55% of the 2,4′-isomer (preferably 1 to 10%), from 0 to 2% of the2,2′-isomer (preferably 0 to 1%) and from 45 to 99% of the 4,4′-isomer(preferably from 90 to 99%), with the sum of the 2,2′-, the 2,4′- andthe 4,4′-isomers totaling 100% by weight of the diphenylmethanediisocyanates. Suitable polyether polyols for the preparation of theprepolymers have molecular weights of from 200 to 8,000 (preferably 240to 4,000), functionalities of from 2 to 6 (preferably 2 to 4), and OHnumbers of from 37 to 1,100 (preferably 56 to 700). It is most preferredthat the polyether polyols 100% of ether units derived from propyleneoxide.

Suitable polyether polyols for use in the preparation of liquid MDIprepolymers containing urethane groups include polyethers prepared, forexample, by the polymerization of epoxides such as ethylene oxide,propylene oxide, butylene oxide, tetrahydrofuran, styrene oxide, orepichlorohydrin, optionally in the presence of Lewis acids such as BF₃,or prepared by chemical addition of such epoxides, optionally added asmixtures or in sequence, to starting components containing reactivehydrogen atoms, such as water, alcohols, or amines. Examples of startingcomponents include ethylene glycol, 1,3- or 1,2-propanediol, 1,2-, 1,3-,or 1,4-butanediol, trimethylolpropane, 4,4′-dihydroxydiphenylpropane,aniline, ammonia, ethanolamine, or ethylene diamine. Sucrose polyethersof the type described, for example, in German Offenlegungschriften1,176,358 and 1,064,938 may also be used according to the invention.Polyethers modified by vinyl polymers of the kind obtained, for example,by the polymerization of styrene and acrylonitrile in the presence ofpolyethers (e.g., U.S. Pat. Nos. 3,383,351, 3,304,273, 3,523,093, and3,110,695 and German Patent 1,152,536) are also suitable, as arepolybutadienes containing hydroxyl groups. Particularly preferredpolyether polyols include polyoxyalkylene polyether polyols, such aspolyoxypropylene diol, polyoxybutylene diol, and polyoxytetramethylenediol.

Other suitable polyether polyols for use in the preparation of liquidMDI adducts containing urethane groups include the so-called PHDpolyols, which are prepared by reactions of organic polyisocyanates,hydrazine, and polyether polyols. U.S. Pat. No. 3,325,421 discloses amethod for producing suitable PHD polyols by reacting a stoichiometricor substoichiometric quantity (relative to diamine) of polyisocyanatedissolved in a polyol having a molecular weight of at least 500 and ahydroxyl number of no more than 225. See also U.S. Pat. Nos. 4,042,537and 4,089,835.

Suitable polyether polyols for use in the preparation of liquid MDIadducts containing urethane groups also include the so-called polymerpolyols, which are prepared by polymerizing styrene and acrylonitrile-in the presence of a polyether. See, for example, U.S. Pat. Nos.3,383,351, 3,304,273, 3,523,093, 3,652,639, 3,823,201 and 4,390,645.

Most preferred polyethers are polyoxypropylene polyethers that do notcontain ethylene glycol units.

Suitable polyether polyols to be used as component (2)(a) in the presentinvention include those polyether polyols having a functionality ofabout 2 to about 4, preferably about 3, a (number average) molecularweight of 200 to about 8,000, preferably between 240 and 4,000 and mostpreferably about 450 to 500 and a hydroxyl number of 14 to 1,120,preferably of about 42 to about 700, and most preferably about 336 toabout 374, wherein the starter for the polyether polyol contains atleast one amine group, and the starter is alkoxylated with 100% byweight of propylene oxide. Suitable starters for these polyether polyolsinclude, for example, those amine group containing compounds wherein theamine groups are aliphatic, cycloaliphatic and aromatic amine groups,preferably diamines or triamines, and more preferably aliphatic,cycloaliphatic and aromatic diamines having primary or secondary aminegroups. Aromatic diamines typically contain exclusively aromaticallybound primary or secondary amino groups. Some examples of suitablestarter compounds include compounds such as ethylenediamine, toluenediamine, triethanolamine, diethanolamine, monoethanolamine,diphenylmethane diamine, 2,4-diaminomesitylene,1,3,5-triethyl-2,4-diaminobenzene,1,3,5-triisopropyl-2,4-diaminobenzene,1-methyl-2,4-diethyl-2,4-diaminomesitylene,1-methyl-2,6-diaminomesitylene,4,6-dimethyl-2,-ethyl-1,3-diaminobenzene,3,5,3′,5′-tetraethyl4,4-diaminodiphenylmethane,3,5,3′,5′-tetraisopropyl4,4′-diaminodiphenylmethane,3,5-diethyl-3′,5′-diisopropyl-4,4′-diaminodiphenylmethane,1,4-diaminobenzene, 2,4-diaminotoluene, 2,4′- and/or4,4′-diaminodiphenylmethane, 3,3′-dimethyl-4,4′-diaminodiphenylmethane,4,4′-diaminodiphenyl propane (-2,2), t-butyl toluene diamine,1-methyl-3,5-bis-(methylthio)-2,4- and/or 2,6-diaminobenzene, andmixtures thereof. Preferred compounds include triethanolamine,diethanolamine, monoethanolamine, and diethyl toluene diamines such as,for example, 1-methyl-3,5-diethyl-2,4-diaminobenzene,1-methyl-3,5-diethyl-2,6-diaminobenzene, and mixtures thereof.

Suitable low unsaturation polyether polyols to be used as component(2)(b) in the present invention include those polyether polyols whereinthe unsaturation is preferably less than 0.01 meq/g, most preferablyless than 0.008 meq/g, and having an OH functionality of about 2, amolecular weight of about 250 to about 8,000, preferably from about 500to about 3,000 and most preferably about 1,000 to about 2,000, and ahydroxyl number of about 14 to about 448, preferably about 37 to about224 and most preferably about 56 to about 112, wherein the startercomprises water or an organic compound with at least two hydroxyl groupsand the starter is alkoxylated with 100% by weight of propylene oxide.Suitable starters for these low unsaturation polyether polyols include,for example, water, ethylene glycol, propylene glycol, dipropyleneglycol, butylene glycol, 1,6-hexanediol, dimethylol cyclohexane, etc.Low unsaturation polyether polyols are known and described in, forexample, U.S. Pat. Nos. 5,576,382, 5,670,601, 5,677,413, 5,689,012,5,700,847, and 5,763,642, the disclosures of which are hereinincorporated by reference, details, and suitable catalysts and processesfor the preparation of these low unsaturation polyether polyols aredescribed in, U.S. Pat. Nos. 5,470,813 and 5,482,908, the disclosures ofwhich are herein incorporated by reference.

The unsaturation of the polyether polyol may be measured by titration inaccordance with ASTM D 2849-69, “TESTING URETHANE FOAM RAW MATERIALS”,and is expressed as milliequivalents of unsaturation per gram of polyol,or “meq/g”.

Suitable isocyanate-reactive components to be used as component (2)(c)in the present invention include, for example, one or more polyetherpolyols having an OH functionality of about 3 to about 6 (preferablyabout 3 to about 4), a molecular weight of about 400 to about 3,000(preferably about 500 to about 1,000 and most preferably about 600 toabout 800), and a hydroxyl number of about 56 to about 840 (preferablyabout 168 to about 448, and most preferably about 210 to about 373),wherein the starter comprises an organic compound with at least threehydroxyl groups and the starter is alkoxylated with 100% by weight ofpropylene oxide. It is preferred that these organic compounds used asstarters are free of amine groups. Suitable starters for these compoundsinclude, for example, glycerol, trimethylolpropane, pentaerythritol,sorbitol, sucrose, etc.

Suitable isocyanate-reactive components to be used as component (2)(d)in the present invention include low molecular weight diols and triols,specifically those diols and triols having an equivalent weight of from31 to 99. Some examples of suitable diols and triols to be used ascomponent (2)(d) in the present invention include compounds such asglycerol, 2-methyl-1,3-propanediol, ethylene glycol, 1,2- and1,3-propanediol, 1,3- and 1,4- and 2,3-butane-diol, 1,6-hexane-diol,1,10-decanediol, diethylene glycol, triethylene glycol, tetraethyleneglycol, dipropylene glycol, tripropylene glycol, neopentyl glycol,cyclohexane-dimethanol, 2,2,4-trimethylpentane-1,3-diol,1,4-ethoxy(β-hydroxybenzene), and mixtures thereof. Preferred diolsinclude, for example, 1,4-butanediol, ethylene glycol, diethyleneglycol, trimethylol propane, 1,4-ethoxy(β-hydroxy-benzene), and mixturesthereof.

Suitable fillers for the present invention include those fillers havinga density of less than 1 g/cm³, preferably less than 0.7 g/cm³, and mostpreferably from 0.2 to 0.5 g/cm³. Suitable fillers include glass hollowspheres, hollow thermoplastic spheres composed of acrylic type resinssuch as polymethylmethacrylate, acrylic modified styrene, polyvinylidenechloride or copolymers of styrene and methyl methacrylate; phenolicresins; silica, ceramic or carbon spheres that are very light in weightand act as a lightweight filler in the syntactic foam. Some commerciallyavailable microspheres include Expancel 551 DE, which is available fromExpancel Inc.; Z-Light W-1000 from Zeelan Industries; Dualite M6032AEwhich is from Pierce & Stevens Corporation; Scotchlite S-series, whichis from 3-M; and QCEL 300 and QCEL 650, which are available from the PQCorporation. The Expancel and Dualite type microspheres are bothexpandable and hollow microspheres consisting of a thin shell of acopolymer of vinyl chloride, vinylidene chloride, and/or acrylonitrile,the shell of the Z-Light W-1000 microsphere is ceramic and theScotchlite and QCEL microspheres consisting of glass shells. Theinterior of the Expancel and Pierce & Stevens microspheres typicallycontain a volatile hydrocarbon, which is typically isobutane, isopentaneor cyclopentane, but also could be made with custom low boilingsolvents, if necessary. The ceramic and glass microspheres usuallycontain air, but may contain vacuum. It is preferred to use glass hollowmicrospheres in the present invention.

Methods for the production of these hollow microspheres are well knownin the art.

The reaction mixture also contains a catalyst (4) for catalyzing thereaction between isocyanate groups and hydroxyl groups (i.e., a urethanecatalyst). Such catalysts are well known in the art. Furthermore, thecomposition should not contain a catalyst which would catalyze thereaction between an isocyanate group and water. Suitable catalysts forthe present invention are organo-metal compounds. Preferred catalystsare organic tin compounds. The organic tin compounds used preferablyinclude tin(II) salts of carboxylic acids such as, for example, tin(II)acetate, tin(II) octoate, tin(II) ethyl hexoate and tin(II) laurate, andtin(IV) compounds such as dibutyl tin oxide, dibutyl tin dichloride,dibutyl tin diacetate, dibutyl tin dilaurate, dibutyl tin dimaleate,dioctyl tin diacetate and the like. Preferred compounds to be used ascatalysts in the present invention include compounds such as dimethyltindilaurate, dibutyltin dilaurate, dimethyltin diacetate, dibutyltindiacetate, dimethyltin dimaleate, dibutyltin dimaleate.

As used herein, the term molecular weight refers to number averagemolecular weight.

The following examples further illustrate details for the preparationand use of the compositions of this invention. The invention, which isset forth in the foregoing disclosure, is not to be limited either inspirit or scope by these examples. Those skilled in the art will readilyunderstand that known variations of the conditions and processes of thefollowing preparative procedures can be used to prepare thesecompositions. Unless otherwise noted, all temperatures are degreesCelsius and all parts and percentages are parts by weight andpercentages by weight, respectively.

EXAMPLES

Isocyanate A: polymethylene poly (phenylisocyanate) having (Comparison)an NCO content of about 31.5%, a functionality of 2.8 and a viscosity at25° C. of 200 mPa·s.

Isocyanate B: an allophanate modified isocyanate having a functionalityof about 2, an NCO group content of about 23%, and a viscosity betweenabout 400 and 650 mPa·s. This isocyanate was stable for at least 30 daysat temperatures of 5° C. or greater. This isocyanate was prepared bycharging (a) 100 parts (pbw) of diphenylmethane diisocyanate comprisingmore than about 98% by weight of the 4,4′-isomer and less than about 2%of the 2,4′-isomer, and (b) 7.76 parts of 2-methyl-1-propanol, to astirred reactor, and heating to 600C. Then, 0.01 part of zincacetylacetonate was added, and the stirred reaction mixture was heatedto 90° C. After one hour at 90° C. the NCO group content was about 23%.The reaction mixture was cooled to 60° C. and 0.025 part of benzoylchloride was added. The reaction mixture was then cooled to 25° C.

Polyol A: a monoethanolamine started propylene oxide polyether polyol,having an OH number of about 350, a functionality of about 3 and anumber average molecular weight of about 480.

Polyol B: a glycerin started propylene oxide polyether polyol, having anOH number of about 250, a functionality of about 3 and a number averagemolecular weight of about 670.

Polyol C: a propylene glycol started propylene oxide having an OH numberof 56, a functionality of about 2 and a molecular weight of about 2000,and no more than about 0.007 meq/g unsaturation.

Catalyst A: dimethyltin dilaurate, commercially available as FomrezUL-28 from Witco.

Glass Bubbles: Scotchlite-38 glass bubbles having a density of 0.38g/cc, commercially available from 3M.

The following polyol blend was used in the examples:

Polyol Blend I: 10 pbw Polyol A 45 pbw Polyol B 45 pbw Polyol C 0.01 pbwCatalyst A

The polyurethane castings in Examples 1 to 6 were prepared according tothe following procedure.

The different isocyanates were hand mixed with 200 g of Polyol Blend Icontaining between 30 and 50% glass hollow spheres (3M Scotchlite glassbubbles(S-38) 0.38 g/cc) at an NCO:OH equivalent ratio of 1.05:1.00 at25-30° C. for about 2 minutes. The ratios by weight are given inTable 1. The mixture was then poured into a mold (6 in.×6 in.×0.125 in.)that was pre-heated to 60° C., and the samples were allowed to cure atroom temperature for 16 hours before demolding. The samples were storedfor at least 1 week at room temperature in a temperature and humiditycontrolled environment, and then tested for various physical andmechanical properties. The results are shown in Table 2.

TABLE 1 Composition of Examples 1-6: Example 1 2 3 4 5 6 Polyol Blend I*200 200 200 200 200 200 Iso A* 85.4 85.4 85.4 Iso B* 108 108 108 GlassBubbles* 60 80 100 60 80 100 Catalyst A 0.003 0.003 0.003 0.003 0.0030.003 Gel time (mins) 3:30 3:30 3:30 3:15 3:15 3:15 Demolding time(mins) 8:00 8:00 8:00 7:00 7:00 7:00 All parts for Polyol Blend I, IsoA, Iso B, Glass Bubbles and Catalyst A in Table 1 are given in grams.*All materials in Examples 1-6 were at 40° C.. All mold temperatures forExamples 1-6 were 60° C..

Gel vs. Demolding Times at Different Catalyst Levels* Isocyanate B (g)59 59 59 59 59 59 Polyol Blend I (g) 100 100 100 100 100 100 GlassBubbles (g) 30 30 30 30 30 30 Catalyst A 0.0 0.001 0.015 0.02 0.05 0.1Gel Time (mins) 24 hrs** 5 hrs** 3:15 2:30 1:00 Gelled while mixingDemolding Time (mins) Not 24 hrs 7:00 6:30 2:00 N.A possible *all rawmaterials and molds were maintained at ambient temperature (i.e. 22° C.)**surface bubbles

These experiments clearly indicate that a minimum amount of organo metalcatalyst is required to obtain a desirable relation between gel time anddemolding time.

In Table 2, Examples 4, 5 and 6, which are representative of the presentinvention, show considerably lower water absorption as measured by %gain in weight after storage under water. Also, at about the samehardness and density as Examples 1, 2 and 3, respectively, the physicalproperties of Examples 4, 5 and 6 are substantially improved.

TABLE 2 Physical testing Results Water Absorption Example 1 2 3 4 5 6Salt Water Testing RT/24 hrs. % gain 1.20 1.51 1.37 0.93 1.15 1.2850C/24 hrs. % gain 1.18 1.06 1.30 1.12 1.34 1.46 RT/168 hrs. % gain 2.432.96 2.72 1.98 1.97 2.11 50C/168 hrs. % gain 2.45 2.64 3.17 1.97 2.192.22 Fresh Water Testing RT/24 hrs. % gain 0.31 0.34 0.40 0.20 0.19 0.27RT/168 hrs. % gain 1.06 1.28 1.36 0.66 0.65 1.02 Tensile PropertiesTensile 981 1154 1264 1534 1615 1750 strength (psi) % elongation 31 2113 48 46 45 Split Tear pli 34 26 20 105 81 101 Die “C” Tear pli 179 244168 327 328 355 Shore A 5 sec. 94 98 97 96 96 97 Shore D 5 sec. 35 53 4550 50 50 Taber Abrasion Wt loss (mg) 2402 2786 3551 652 1270 1147Rebound % 22 44 30 45 40 36 Density lb/ft3 50 48 45 50 48 46

At about the same hardness and density, the use of liquiddiphenylmethane diisocyanate vs. polymeric MDI, combined with the use oflow unsaturation difunctional polyethers results in syntactic foamswhich have the following advantages:

much higher tensile strength and elongation (about 50%).

much higher tear strength (on the average 3 times higher).

much lower Taber abrasion (30 to 50%).

considerably lower water absorption (25 to 50% in fresh water, and 20 to30% in salt water).

Although the invention has been described in detail in the foregoing forthe purpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention except as it may be limited by the claims.

What is claimed is:
 1. A syntactic foam comprising the reaction productof: (1) a liquid diphenylmethane diisocyanate having an NCO groupcontent of from about 10 to about 33.6% and a viscosity from about 10 toabout 5,000 mPa·s @ 25° C., with (2) an isocyanate-reactive componentcomprising: (a) at least 10% by weight of one or more polyether polyolshaving a functionality of 2 to 4, a molecular weight of 200 to 8,000,and a hydroxyl number of 14 to 1,120, wherein at least one amine groupis present in the starter for said polyether polyol, and the starterbeing alkoxylated by 100% by weight of propylene oxide; (b) at least 20%by weight of one or more low unsaturation polyether polyols having an OHfunctionality of about 2, a molecular weight of 250 to 8,000, and ahydroxyl number of 14 to 448, wherein the starter for said lowunsaturation polyether polyol comprises water or an organic componentcontaining two hydroxyl groups, and the starter being alkoxylated with100% by weight of propylene oxide; (c) at least 20% by weight of one ormore polyether polyols having an OH functionality of about 3 to 6, amolecular weight of about 400 to about 3,000, and an hydroxyl number ofabout 56 to about 840, wherein the starter for said polyether polyolcomprises an organic compound containing at least three hydroxyl groups,and the starter being alkoxylated with 100% by weight of propyleneoxide; and, optionally, (d) up to 10% by weight of one or more lowmolecular weight diols and/or triols having an equivalent weight of from31 to 99; wherein the %'s by weight of (2)(a), (2)(b), (2)(c) and (2)(d)totals 100% by weight of component (2); (3) from 10 to 70% by weight,based on the combined weight of components (1), (2) and (3), of a fillerhaving a density of less than 1 g/cm³; and (4) at least oneorgano-metallic catalyst in the amount of about 0.001 to about 1% byweight, based on 100% by weight of (2); wherein the relative amounts ofcomponents (1) and (2) are such that the isocyanate index is from about90 to about
 120. 2. The syntactic foam of claim 1, wherein (1) saidliquid diphenylmethane diisocyanate comprises up to 70% by weight of2,4′-diphenylmethane diisocyanate, no more than 2% by weight of2,2′-diphenylmethane diisocyanate, and the balance being4,4′-diphenylmethane diisocyanate, such that the sum of the 2,4′-MDI,the 2,2′-MDI and the 4,4′-MDI totals 100% by weight of the liquiddiphenylmethane diisocyanate.
 3. The syntactic foam of claim 2, wherein(1) said liquid diphenylmethane diisocyanate comprises less than 10% byweight of 2,4′-diphenylmethane diisocyanate.
 4. The syntactic foam ofclaim 1, wherein (1) said liquid diphenylmethane diisocyanate comprisesallophanate modified diphenylmethane diisocyanate.
 5. The syntactic foamof claim 1, wherein (1) the liquid diphenylmethane diisocyanatecomprises carbodiimide groups and/or uretonimine groups.
 6. Thesyntactic foam of claim 2, wherein (1) the liquid diphenylmethanediisocyanate comprises the reaction product of diphenylmethanediisocyanate with a polyether polyol containing at least 80% by weightof ether units derived from propylene oxide.
 7. The syntactic foam ofclaim 6, wherein the polyether polyol comprises dipropylene glycol,tripropylene glycol or mixtures thereof.
 8. The syntactic foam of claim1, wherein (2) said isocyanate-reactive component comprises (a) from 10to 30% by weight of one or more polyether polyols having a functionalityof about 3, a molecular weight of between about 240 and 4,000, and ahydroxyl number of about 42 to about 700; (b) from about 30 to about 80%by weight of one or more low unsaturation polyether polyols having an OHfunctionality of about 2, a molecular weight of from about 500 to about3,000 and a hydroxyl number of about 37 to about 224; and (c) from about30 to about 80% by weight of one or more polyether polyols having an OHfunctionality of about 3 to about 4, a molecular weight of about 500 toabout 1,000 and an OH number of about 168 to about
 448. 9. A process forpreparing a syntactic foam, comprising reacting: (1) a liquiddiphenylmethane diisocyanate having an NCO group content of from about10 to about 33.6% and a viscosity from about to about 5,000 mPa·s @ 25°C., with (2) an isocyanate-reactive component comprising: (a) at least10% by weight of one or more polyether polyols having a functionality of2 to 4, a molecular weight of 200 to 8,000, and a hydroxyl number of 14to 1,120, wherein at least one amine group is present in the starter forsaid polyether polyol, and the starter being alkoxylated by 100% byweight of propylene oxide; (b) at least 20% by weight of one or more lowunsaturation polyether polyols having an OH functionality of about 2, amolecular weight of 250 to 8,000, and a hydroxyl number of about 14 to448, wherein the starter for said low unsaturation polyether polyolcomprises water or an organic component containing two hydroxyl groups,and the starter being alkoxylated with 100% by weight of propyleneoxide; (c) at least 20% by weight of one or more polyether polyolshaving an OH functionality of about 3 to 6, a molecular weight of about400 to about 3,000, and an hydroxyl number of about 56 to about 840,wherein the starter for said polyether polyol comprises an organiccompound containing at least three hydroxyl groups, and the starterbeing alkoxylated with 100% by weight of propylene oxide; and,optionally, (d) up to 10% by weight of one or more low molecular weightdiols and/or triols having an equivalent weight of from 31 to 99;wherein the %'s by weight of (2)(a), (2)(b), (2)(c) and (2)(d) totals100% by weight of component (2); (3) from 10 to 70% by weight, based onthe combined weight of components (1), (2) and (3), of a filler having adensity of less than 1 g/cm³; and (4) at least one organo-metalliccatalyst in the amount of about 0.001 to about 1% by weight, based on100% by weight of component (2); wherein the relative amounts ofcomponents (1) and (2) are such that the isocyanate index is from about90 to about
 120. 10. The process of claim 9, wherein (1) said liquiddiphenylmethane diisocyanate comprises up to 70% by weight of2,4′-diphenylmethane diisocyanate, no more than 2% by weight of2,2′-diphenylmethane diisocyanate, and the balance being4,4′-diphenylmethane diisocyanate, such that the sum of the 2,4′-MDI,the 2,2′-MDI and the 4,4′-MDI totals 100% by weight of the liquiddiphenylmethane diisocyanate.
 11. The process of claim 10, wherein (1)said liquid diphenylmethane diisocyanate comprises less than 10% byweight of 2,4′-diphenylmethane diisocyanate.
 12. The process of claim 9,wherein (1) said liquid diphenylmethane diisocyanate comprisesallophanate modified diphenylmethane diisocyanate.
 13. The process ofclaim 9, wherein (1) the liquid diphenylmethane diisocyanate comprisescarbodiimide groups and/or uretonimine groups.
 14. The process of claim10, wherein (1) the liquid diphenylmethane diisocyanate comprises thereaction product of diphenylmethane diisocyanate with a polyether polyolcontaining at least 80% by weight of ether units derived from propyleneoxide.
 15. The process of claim 14, wherein the polyether polyolcomprises dipropylene glycol, tripropylene glycol or mixtures thereof.16. The process of claim 9, wherein (2) said isocyanate-reactivecomponent comprises (a) from 10 to 30% by weight of one or morepolyether polyols having a functionality of about 3, a molecular weightof between about 240 and 4,000, and a hydroxyl number of about 42 toabout 700; (b) from about 30 to about 80% by weight of one or more lowunsaturation polyether polyols having an OH functionality of about 2, amolecular weight of from about 500 to about 3,000 and a hydroxyl numberof about 37 to about 224; and (c) from about 30 to about 80% by weightof one or more polyether polyols having an OH functionality of about 3to about 4, a molecular weight of about 500 to about 1,000 and an OHnumber of about 168 to about
 448. 17. A process for preparing a pipeinsulated with a syntactic foam, comprising: (I) placing a steel pipe inthe center of a cylindrical mold with the diameter of the mold beinglarger than the diameter of the pipe, wherein the difference in diameterbetween the pipe and the mold determines the thickness of the syntacticfoam to be applied; (II) pouring a liquid polyurethane reaction mixturecontaining a filler around the steel pipe in the mold, wherein saidliquid polyurethane reaction mixture is formed by: (A) blending (3) afiller having a density of less than 1 g/cm³ with (1) a liquiddiisocyanate component and/or (2) an isocyanate-reactive component, (B)adding (4) an organo-metallic catalyst to the isocyanate-reactivecomponent which may or may not contain a filler; and (C) mixing theliquid diisocyanate component with the isocyanate-reactive component,wherein: (1) said liquid diisocyanate component comprises liquiddiphenylmethane diisocyanate having an NCO group content of from about10 to about 33.6% and a viscosity from about 10 to about 5,000 mPa·s @25° C., with (2) an isocyanate-reactive component comprising: (a) atleast 10% by weight of one or more polyether polyols having afunctionality of 2 to 4, a molecular weight of 200 to 8,000, and ahydroxyl number of 14 to 1,120, wherein the starter for said polyetherpolyol comprises at least one amine group, and said starter beingalkoxylated by 100% by weight of propylene oxide; (b) at least 50% byweight of one or more low unsaturation polyether polyols having an OHfunctionality of about 2, a molecular weight of 250 to 8,000, and ahydroxyl number of 14 to 448, wherein the starter comprises water or anorganic component containing at least two hydroxyl groups, and saidstarter being alkoxylated with 100% by weight of propylene oxide; (c) atleast 20% by weight of one or more polyether polyols having an OHfunctionality of about 3 to about 6, a molecular weight of about 400 toabout 3,000, and an hydroxyl number of about 56 to about 840, whereinthe starter for said polyether polyol comprises an organic compoundcontaining at least three hydroxyl groups, and said starter beingalkoxylated with 100% by weight of propylene oxide; and, optionally, (d)up to 10% by weight of one or more low molecular weight diols and/ortriols having an equivalent weight of from 31 to 99, wherein the %'s byweight of (2)(a), (2)(b), (2)(c) and (2)(d) totals 100% by weight ofcomponent (2); (III) allowing the liquid polyurethane reaction mixturecontaining the filler cure to form a solid polyurethane containing afiller, which encapsulates the steel pipe; and (IV) demolding thepolyurethane encapsulated steel pipe, thereby yielding a syntactic foaminsulated pipe.
 18. A syntactic foam insulated pipe produced by theprocess of claim 17.